stdio: make internal symbols static/hidden

Although header libc/stdio/local.h declares the macros and private
variables of stdio, there are several internal symbols exposed
unexpectedly.

Change-Id: Ie7a07f85b70322fb9cd05b3c8e1bcc416061eb4b

libc/stdio/fgetln.c

@@ -43,7 +43,7 @@
  * so we add 1 here.
 #endif
  */
-int
+static int
 __slbexpand(FILE *fp, size_t newsize)
 {
 	void *p;

libc/stdio/findfp.c

@@ -55,7 +55,7 @@ static FILE usual[FOPEN_MAX - 3];
 static struct __sfileext usualext[FOPEN_MAX - 3];
 static struct glue uglue = { 0, FOPEN_MAX - 3, usual };
 
-struct __sfileext __sFext[3];
+static struct __sfileext __sFext[3];
 FILE __sF[3] = {
 	std(__SRD, STDIN_FILENO),		/* stdin */
 	std(__SWR, STDOUT_FILENO),		/* stdout */

libc/stdio/flockfile.c

@@ -191,7 +191,7 @@ funlockfile(FILE * fp)
 
 
 /* called from fclose() to remove the file lock */
-void
+__LIBC_HIDDEN__ void
 __fremovelock(FILE*  fp)
 {
     LockTable*  t = lock_table_lock();

libc/stdio/fvwrite.c

@@ -44,7 +44,7 @@
  * This routine is large and unsightly, but most of the ugliness due
  * to the three different kinds of output buffering is handled here.
  */
-int
+__LIBC_HIDDEN__ int
 __sfvwrite(FILE *fp, struct __suio *uio)
 {
 	size_t len;

libc/stdio/mktemp.c

@@ -65,7 +65,7 @@ mkdtemp(char *path)
 
 char *_mktemp(char *);
 
-char *
+__LIBC_HIDDEN__ char *
 _mktemp(char *path)
 {
 	return(_gettemp(path, (int *)NULL, 0, 0) ? path : (char *)NULL);